Mercutio switches to sarcasm here and begins to mock Romeo's vision of love. Mercutio says: "And, to sink in it, should you burden love -- Too great oppression for a tender thing- (1.4.23-24). Mercutio tells Romeo that if he is going to blame love as the burden of his state of mind, then he is only going to sink deeper into love. Mercutio also uses a double entendre for this quote, meaning also that if Romeo is to have sex with the woman that he loves, then he will sink into her and burden her body. The general idea of Mercutio's speech seems to be that Romeo is taking himself too seriously and he needs to lighten up before he drives himself insane.
Romeo doesn't seem to get the point though and complains that love is not tender, but rough and that it "pricks like a thorn- (1.4.26). Mercutio responds with "Prick love for pricking, and you beat love down- (1.4.28). Mercutio views Romeo's lovesickness as being the result of the lack of sex, and he seems to think that if Romeo were to have sex then he would get over his affliction of being in love. Later on in the scene, Mercutio again mocks Romeo's love when he says "we'll draw thee from the mire Of this sir-.
reverence love, wherein thou stick'st Up to the ears- (1.4.40-43). Here, Mercutio is telling Romeo that he thinks Romeo's love is, essentially, a heap of worthless emotion and that he, Mercutio, will do whatever he can to draw Romeo out of the pile of it that he has gotten himself stuck in. Mercutio's language is so vulgar because he views it as the most blunt way to draw Romeo out of his shell, and he is also used, in a sense, as a sort of comic relief similar to that of the Nurse or Friar Lawrence.
Mercutio's Queen Mab speech occurs after Romeo states that he doesn't wish to go the party at the Capulet's. He believes that Romeo is just whining and saying that he doesn't wish to go, although it seems that Romeo may have a general premonition that things are going to go badly if he appears there when he says "And we mean well in going to this masque, But tis no wit to go.
